I would suggest replacing part that's broken, it's not that complicated, or if u'r not confident, take it to shop for repair especially if you planning to buy gearbox for classic army gun.
Iv replaced the trigger contact, rewired the whole gearbox, tried firing it worked fine then a whining sound, opened the gearbox and the gears have lost a few teeth. Orderd a new tappet plate and a new set of gears